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M1 Repairs


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Hi there,

I'm looking to have a go at repairing m1's

Just wondering can anyone program fresh M1 pal/Gals?

I've got a few boards to work on and I'd like to start out fresh chips if possible.

Also any help on M1 tips or schematics is really appreciated thnx!

Edited by MattyL
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M1A all finished and the machine back to life. 😎 20200313_105646.mp4

key to maygay is test the RAM pins with a logic probe while there is no card in.  They should all be floating (not HI or LO) .  If any are showing a signal theres a shorted IC on the databus. Sec

Here's two of my latest boards I've repaired while off work furloughed. Both were not to bad battery damage really.  One had burned out track under the meter driver which I've not seen before...

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key to maygay is test the RAM pins with a logic probe while there is no card in.  They should all be floating (not HI or LO) .  If any are showing a signal theres a shorted IC on the databus.

Second key is a magic number - 20C0. In nearly al M1 games the very first instruction in ROM ( at 2800h)  loads a register with 1.  The next instruction after that writes the value in the register to location 20C0.  That happens to be pin 4 of U11 on 1A and 1B which sets IOenable to HI , ie turns it off.  That in turn sets RAM enable at the PAL chip ON.  If you cant do that, you cant peform a RAM test.

just in case it helps ,  on maygay  RAM sits at 0000-1FFF, the IO sits 2000-27FF and the ROM fills the address space after that (2800 and up)

 

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On 10/13/2019 at 1:22 PM, MAGIK said:

key to maygay is test the RAM pins with a logic probe while there is no card in.  They should all be floating (not HI or LO) .  If any are showing a signal theres a shorted IC on the databus.

Second key is a magic number - 20C0. In nearly al M1 games the very first instruction in ROM ( at 2800h)  loads a register with 1.  The next instruction after that writes the value in the register to location 20C0.  That happens to be pin 4 of U11 on 1A and 1B which sets IOenable to HI , ie turns it off.  That in turn sets RAM enable at the PAL chip ON.  If you cant do that, you cant peform a RAM test.

just in case it helps ,  on maygay  RAM sits at 0000-1FFF, the IO sits 2000-27FF and the ROM fills the address space after that (2800 and up)

 

Thanks Majik I'm sort of getting my head round that.

Bad pal/Gal = no ram test?

I'm replacing U11 I'll try and trace that out and log it into my brain.

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1 minute ago, -Crest- said:

Glad to help it’s good that they were posted on here years ago, a lot people hide schemics unfortunately 

Do you know if it's possible to down load them and get them printed out in A3? All ready spotted a different diode on one board.

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Hopefully they are easy enough to fix but I have a act for picking bad boards 

This is one I swapped to James hardy last year. Magik loved this one :lol: 

Looked quite clean to haha

 

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3 minutes ago, MattyL said:

Do you know if it's possible to down load them and get them printed out in A3? All ready spotted a different diode on one board.

You Should be able to just save the images and print them out?

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I started my first board tonight here's where I'm at.

I'm planning to repair the tracks, refit new IC's when they turn up. One repair needs to go through the via onto the back.

Change that diode on D30 to a 1N.

Change the old transistor q1.

Try it

Open to any suggestions as usual.

Also looking for the hex file of the m1b test Rom.

Thanks

20191014_224148.jpg

Edited by MattyL
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18 hours ago, MattyL said:

Change that diode on D30 to a 1N.

Nope, you will find the BAS48 fitted has a lower forward voltage and therefore much better than the 1N4148 as not so much voltage drop across it.

the schematics are not always correct due to the continuous improvement policy all company's have through the lifetime of the product

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44 minutes ago, Andrew96_ said:

Nope, you will find the BAS48 fitted has a lower forward voltage and therefore much better than the 1N4148 as not so much voltage drop across it.

the schematics are not always correct due to the continuous improvement policy all company's have through the lifetime of the product

Ok I'll not do that then... Thanks this must be a later board.

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your also find a yellow capacitor 'added in' on the topside (its at a angle to the other components) and a resistor on the underside  near the coin mech terminals that is not on the circuit diagram, this is because when they made the M1b boards they got it wrong! so these are added to straighten up the pulse edges for the coin mech strobe signals! remove them and it won't work! this was not  problem with the earlier M1a boards as they got the switch strobes perfect! 

Don't believe everything the circuit diagrams tell you!!!!

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1 hour ago, Andrew96_ said:

your also find a yellow capacitor 'added in' on the topside (its at a angle to the other components) and a resistor on the underside  near the coin mech terminals that is not on the circuit diagram, this is because when they made the M1b boards they got it wrong! so these are added to straighten up the pulse edges for the coin mech strobe signals! remove them and it won't work! this was not  problem with the earlier M1a boards as they got the switch strobes perfect! 

Don't believe everything the circuit diagrams tell you!!!!

Yeah thanks, the resistor I thought must be a mod. The cap I put down to an after thought because it was angled. There's also x1 link wire on the back and x1 on the ESP card which I presume are mods too?

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Ok so here's the board tonight. I'm pretty sure I've got all the broken areas, I've also added more repair wires just to be 110% the tracks hold up from eyelet/track/eyelet.

Hope it's enough... I really want this board to work!

 

20191015_225927.jpg

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